Squirrels relocated to build owl homes

San Diego Zoo's latest local conservation program has relocated more than 350 squirrels to three sites in East County that are thought to be suitable habitat for squirrels and owls.

/ Ken Bohn/San Diego Zoo Global

San Diego Zoo's latest local conservation program has relocated more than 350 squirrels to three sites in East County that are thought to be suitable habitat for squirrels and owls.

San Diego Zoo's latest local conservation program has relocated more than 350 squirrels to three sites in East County that are thought to be suitable habitat for squirrels and owls. (/ Ken Bohn/San Diego Zoo Global)

It might sound like a spoof, but San Diego Zoo officials this week are crowing about the early success of a novel ground squirrel relocation project in the county.

Why might 350 of the noted pests need new digs near Jamul, Otay Mesa and Sweetwater?

It turns out the critters are critical to the welfare of burrowing owls, which rely on squirrel holes for shelter. The zoo goes so far as to call squirrels "grasslands engineers."

The burrowing owl population has plummeted in San Diego County and across the West, prompting zoo scientists to team with San Diego State University, the U.S. Fish and Wildlife Service and the California Department of Fish and Game on a conservation project that one scientist called the first of its kind. The first year will cost about $240,000, paid for by grants and the zoo.

Owl habitat projects are common, but they typically involve people creating and maintaining artificial burrows for the birds in areas where they've been edged out by development.

"The whole idea is to get more hands-off," said Colleen Lenihan at the zoo's Institute for Conservation Research. "We want the squirrels to do the work for us."

Burrowing owls are listed as a species of concern by the U.S. Fish and Wildlife Service, but the population is crashing and may require listing as an endangered species if recent trends don't turn around. — Ken Bohn/San Diego Zoo Global

Burrowing owls

Measure 7.5 to 10 inches tall with wingspans 21 to 24 inches. Unlike most owls, the male bird is slightly heavier and has a longer wingspan than the females.

Are found in dry, open areas with low vegetation such as grasslands, deserts, farmlands, rangelands, golf courses and vacant lots in urban areas. They once were spread broadly throughout western North America but numbers have declined across all historic ranges in the past 30 years. Outside the United States, the burrowing owls live in Central America, Canada and most of South America.

Feed primarily on insects and small mammals, but also will eat reptiles and amphibians. Burrowing owls hunt while walking or running across the ground and by swooping down from a perch. They catch insects from the air.

Source: Burrowing Owl Conservation Network

Burrowing owls are in trouble because they rely on grasslands with lots of flat ground and low vegetation. Development has reduced suitable spots and ground squirrel eradication programs may have limited burrowing owl nesting sites.

"The re-establishment of California ground squirrels is a critical component of any long-term recovery plan for burrowing owls and the larger ecosystem because squirrels provide vital resources," Lenihan said. "Sites with ground squirrel colonies have a greater diversity of reptiles, amphibians, insects and birds than sites where they are absent."

Concern has grown about burrowing owls as their populations have shriveled. In San Diego County, roughly 600 burrowing owls were counted about 30 years ago, but the best estimate these days in the double digits at only a handful of sites. Click here to read a recent story about their decline.

Ecologists said the owls could rebound quickly under the right circumstances because they lay lots of eggs -- up to 11 per clutch -- and they have adapted to human landscapes.

The multi-agency recovery project involved trapping squirrels from Coronado and Pine Valley in hopes of determining whether coastal or inland critters fare better at the relocation sites. Drop-off spots were chosen for a variety of reasons including that owls live nearby and may recolonize if they have more hideouts.

Squirrels were given "starter holes" and then left on their own to make Swiss cheese out of the terrain. "The idea is that they will go out and dig a bunch of natural holes," Lenihan said.

This week, scientists went back to a release site near Jamul and trapped squirrels to see what's happened to their numbers over the past few months. Lenihan was upbeat about the prospects.

"We are catching a lot of squirrels that are still hanging around," she said.

And, she added, "We are having some (owl) visitors."

The real test will be how the squirrels and the owls fare over the next year. As that becomes clear, Lenihan and others will decide whether the project is worth expanding.